The relevance of domain studies to both intrinsic and technical magnetic properties and the reasons for the continued interest and activity in the subject are discussed. The particular advantages of certain of the many methods of observing domains are noted, without attempting any comprehensive survey. Reference is made to some recent developments using x‐rays, to the interpretation of powder patterns, and to dynamic studies. There is no general domain theory, i.e., no theory which predicts the domain structure which will exist in a specimen with specified shape and intrinsic properties. However, it is possible to evaluate, with varying degrees of approximation, the energies corresponding to some observed or postulated structures. Domain observations can then be used to verify magnetostatic calculations, and can give measurements of certain intrinsic properties. Also, precise calculations of magnetization curves can be made for postulated structures in the hope that these will elucidate the technical properties of real materials.